1. Field of the Invention
The present invention relates to a method for manufacturing a display device having a stacked-layer structure of thin films, and specifically relates to a process of forming an opening in a thin film in a process of manufacturing a display device.
2. Description of the Related Art
Each of a thin film transistor (hereinafter also referred to as a “TFT”) and an electronic circuit using the thin film transistor is manufactured as follows: various thin films such as a semiconductor film, an insulating film, and a conductive film are stacked over a substrate, and a predetermined pattern is formed by a photolithography technique as appropriate. The photolithography technique is a technique in which a pattern of a circuit or the like which is formed of a material which does not transmit light over a transparent flat plate, a so-called photomask, is transferred to a substrate, by using light. It has been widely used in a process of manufacturing a semiconductor integrated circuit or the like.
A conventional manufacturing process using the photolithography technique requires multiple steps including exposure, development, baking, and peeling only for treating a mask pattern formed of a photosensitive organic resin material called a photoresist. Therefore, the manufacturing cost is inevitably increased as the number of the photolithography processes is increased. In order to solve such a problem, it has been attempted to manufacture a TFT with a smaller frequency of photolithography processes (Reference 1: Japanese Published Patent Application No. 2000-133636). In Reference 1, after a resist mask formed by a photolithography process is used once, it is swelled to expand volume and then used again as a resist mask having a different shape.